Как сделать, чтоб вводились только числа?

//---------------------------------------------------------------------------
 
#include <vcl.h>
#pragma hdrstop
#include <stdio.h>
#include "Unit1.h"
int i;
int h=0;
FILE *xxx;
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
        : TForm(Owner)
{
 struct details{
char name[25];
char type[25];
char number[5];};
details z;
 
 xxx=fopen("Файл.txt","r");
 
 while(!feof(xxx)){
fread(&z,sizeof(details),1,xxx);
 
StringGrid1->Cells[0][h]=z.name;
StringGrid1->Cells[1][h]=z.type;
StringGrid1->Cells[2][h]=z.number;
h++;
i=h;
StringGrid1->RowCount=i;
 
 
}
fclose(xxx);
 
 
}
//---------------------------------------------------------------------------
 
void __fastcall TForm1::BitBtn1Click(TObject *Sender)
{
struct details{
char name[25];
char type[25];
char number[5];};
details z;
 
for(int a=0;a<=25;a++){
z.name[a]='\0';
z.type[a]='\0';}
for(int a=0;a<=5;a++) {
z.number[a]='\0'; }
 
strcpy(z.name,ComboBox1->Text.c_str());
strcpy(z.type,Edit1->Text.c_str());
strcpy(z.number,Edit2->Text.c_str());
 
 
xxx=fopen("Деталь.txt","a");
fwrite(&z,sizeof(details),1,xxx);
fclose(xxx);
 
xxx=fopen("Файл.txt","a");
fwrite(&z,sizeof(details),1,xxx);
fclose(xxx);
 
xxx=fopen("Деталь.txt","r");
fseek(xxx,-sizeof(details),SEEK_END);
fread(&z,sizeof(details),1,xxx);
 
 
StringGrid1->Cells[0][i]=z.name;
StringGrid1->Cells[1][i]=z.type;
StringGrid1->Cells[2][i]=z.number;
 
fclose(xxx);
i++;
xxx=fopen("Деталь.txt","a");
char v='\n';
fwrite(&v,sizeof(char),1,xxx);
fclose(xxx);
StringGrid1->RowCount=i;
 
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Edit2Change(TObject *Sender)
{
 
}
//---------------------------------------------------------------------------